Adhesive materials are used for restorative treatment of teeth. As the adhesive materials, resin-based curable compositions including, for example, a radical-polymerizable monomer and polymerization initiator are generally used.
Conventionally, two major proposals have been made for the resin-based curable compositions in order to improve their adhesiveness to a tooth structure. One of the proposals is related to a radical-polymerizable monomer containing an acid group and intended to improve chemical and physical interaction with a tooth structure to which the composition is adhered. The other is a proposal related to a polymerization initiator intended to efficiently polymerize and cure a curable composition including an acid group-containing radical-polymerizable monomer on a tooth structure.
As dental adhesive materials composed of these resin-based curable compositions, so-called self-etching adhesive materials are commonly used.
Specifically, a self-etching primer and/or bonding material including a polymerizable monomer containing an acid group and hydrophilic polymerizable monomer is applied onto the surface of a tooth structure.
To exhibit sufficient bond strength to a tooth structure, particularly dentin, dental adhesive materials need to cause demineralization effect in which the surface of dentin is dissolved with an acid component, penetration effect in which a polymerizable monomer component penetrates the collagen of dentin, and curing effect in which the penetrated polymerizable monomer component is cured to form a hybrid layer with the collagen.
However, when resin-based curable compositions are adhered to a tooth structure, curing inhibition by oxygen existing at the adhesive interface often decreases the degree of the curing effect among the above demineralization effect, penetration effect, and curing effect, which leads to a failure to obtain sufficient bond strength. Such curing inhibition is more salient when curable compositions are adhered to the dentin of a tooth including a lot of oxygen. Moreover, polymerization inhibition due to dissolved oxygen is particularly salient on the dentin in a root canal of a tooth because the dentin has a high water content.
In recent years, thanks to great progress of light irradiation units, photopolymerization allowing a short-time procedure has become used in restoration treatment with an abutment construction material to fill the inside of a root canal where light cannot reach easily for restoration. However, since light is applied from above and curing proceeds from the top of the filling material, strain and stress due to shrinkage caused by polymerization are likely to concentrate at the interface with a tooth structure to increase a risk of inducing detachment of the filling material.
Conventionally, first light irradiation is carried out after an adhesive material is applied, and second light irradiation is carried out after a filling material is placed. However, there is a growing demand for a system in which a primer is applied, a filling material is then placed without light irradiation of the primer, and photopolymerization is accomplished by one-time light irradiation. This system is exposed to an increased risk of inducing detachment of the filling material. A redox polymerization initiator adapted to the system and capable of effectively reducing the oxygen-induced curing inhibition at the interface with a tooth structure during curing to promote a polymerization and curing reaction has been proposed.
The adhesive kit described in Patent Literature 1 is an example in which high bond strength is achieved by incorporating a transition metal compound in a pretreatment agent and hydroperoxide and pyridylthiourea in an adhesive material. The dental restorative filling kit described in Patent Literature 2 is an example in which high bond strength and storage stability of the material are achieved by including a transition metal compound in a pretreatment agent and hydroperoxide in a filling material and excluding an amine from the pretreatment agent and an aryl borate compound from the filling material.